1. Field of the Invention
This invention relates to absorbent articles, particularly absorbent structures which are useful in personal care products such as disposable sanitary napkins, diapers, incontinence garments, and the like. More particularly, this invention relates to absorbent systems that must manage complex viscous body fluids such as menses.
2. Description of Prior Art
Absorbent articles such as feminine pads or sanitary napkins, diapers and incontinence garments are intended to intake and retain body fluids. Desired performance objectives of these articles include low leakage from the product and a dry feel to the wearer. Currently available products suffer from higher than desired leakage levels, producing stains on clothing, and are not perceived by users to fully deliver on other consumer attributes such as dryness, fit, comfort and continence. Leakage can occur due to a variety of shortcomings in the product, not the least of which is an insufficient rate of fluid uptake by the absorbent system, particularly on the second or third liquid surges. This is particularly problematic with feminine care products intended for overnight use where high loadings are often incurred requiring significant fluid retention capacity in order to hold the majority of the fluid.
Most commercially available sanitary pads have relatively high leakage rates, failing as much as 30% of the time. Such failures are believed to be due to the highly viscous nature of menses and the great variability in delivery volume which results in overloading of the pad in the target area and subsequent leaking. Insufficient distribution of menses is believed to be one of the key causes of the target area overloading.
In the field of urine management in personal care products like diapers, distribution is often provided by materials that have small pores with a narrow pore size distribution. These materials must move the high volume, low viscosity urine insults out of the target area in a time sufficient for the target area to be able to accept the next insult. The movement of urine may be to relatively remote parts of the diaper, overcoming substantial hydrostatic pressure. In contrast thereto, feminine hygiene products experience lower total insult volumes, but the fluid is of greater viscosity, making it more difficult to move the fluid. Distribution materials must be quite different for feminine hygiene products than for products concerned primarily with urine management.
Absorbent articles have typically employed various types of absorbent pads composed of cellulosic fibers. Particular absorbent garments may configure to control the distribution of absorbed liquids. For example, an absorbent article can have a liquid permeable transport layer which is located between a top sheet layer and an absorbent body. In other configurations, a conventional absorbent member can have fluid storage and acquisition zones composed of cellulosic fluff mixed with absorbent gelling particles and may include a dual-layer absorbent core arrangement comprising a bottom fluff pad containing hydrogel particles, and a top fluff pad with little or no hydrogel particles.
Non-woven materials such as carded webs and spunbond webs have been used as the body side liners in absorbent products. Specifically, very open, porous liner structures have been employed to allow liquid to pass through them rapidly and help keep the body skin separated from the wetted absorbent pad beneath the liner. Some structures have incorporated zoned surfactant treatments in preselected areas of the liners to increase the wettability of the preselected regions and thereby control the amount of liquid wet-back onto a wearer""s skin. In addition, other layers of material, such as those constructed with thick, lofty fabric structures, have been interposed between the liner and absorbent pad for the purpose of reducing wet-back.
With conventional fluff-based absorbent structures, such as those discussed above, the cellulosic fibers, when wetted, can lose resiliency and collapse. As a result, the liquid uptake rate of the wetted structures may become too low to adequately accommodate subsequent, successive liquid surges. Where absorbent gelling particles are incorporated between the fibers to hold them apart, the gelling particles swell and do not release the absorbed fluid. Swelling of the particles can then diminish the void volume of the absorbent structure and reduce the ability of the structure to rapidly uptake fluids.
The addition of more absorbent material, such as secondary fluff pledgets, or absorbent gelling particles, has been employed to increase holding capacity. The desired rate of liquid intake within such arrangements, however, may not be sufficiently sustained during successive liquid surges.
Despite the development of absorbent structures as discussed hereinabove, there remains a need for improved absorbent structures which can adequately reduce the incidence of leakage from absorbent products, such as feminine hygiene products. There is a need for an absorbent structure which can provide improved handling of liquid surges and more effectively uptake and retain repeated loadings of liquid during use.
Accordingly, it is one object of this invention to provide a feminine hygiene product having superior distribution and transfer performance to allow movement of menses from a target area and provide comfort, dry feeling, and lower leakage than traditional such products.
It is another object of this invention to provide an overnight use feminine hygiene product having the capacity to hold the majority of fluids resulting from the high loadings which have been observed in such overnight products.
The overnight feminine hygiene products typically are thick maxipads with a 600 gsm basis weight fluff pad and fluff insert, which fluff material is present in the product for aesthetic and pad shaping reasons. It is one object of this invention to provide an absorbent system which enables utilization of the potential fluid storage capacity in the fluff.
It is yet another object of this invention to provide a feminine hygiene product such as an Ultrathin, Maxi, Overnite, Curved, Securehold and the like which provides good distribution and fluid transfer thus promoting absorbency and dryness.
These and other objects of this invention are achieved by a personal care absorbent article comprising a fluid intake/distribution layer, a fluid transfer delay layer disposed beneath the fluid intake/distribution layer, which fluid transfer delay layer enables fluid transfer from the fluid intake/distribution layer resulting in a fluid saturation of less than or equal to about 0.86 g/g/in in the fluid intake/distribution layer, and a pad layer disposed beneath the fluid transfer delay layer having a fluid saturation level essentially equivalent to or greater than 0.06 g/g/inch. The fluid intake/distribution layer is comprised of stabilized, highly wettable fibers arranged to provide capillary pore sizes and a degree of wettability ideally suited to wick visco-elastic fluids, which layer, when exposed to visco-elastic fluids and simulants, demonstrates improved fluid distribution performance in terms of the distance wicked, the wicking rate, as well as the amount of fluid moved. The fluid intake/distribution layer comprises a class of distribution materials composed of stabilized, highly wettable fibers arranged to provide capillary pore sizes and a degree of wettability ideally suited to wick visco-elastic fluids. Stabilization may be accomplished by the use of liquid binders, binder fibers, thermally, or in any other method known to those skilled in the art. When exposed to a visco-elastic fluid or fluid simulant, these materials demonstrate improved fluid distribution performance for distance wicked, wicking rate and amount of fluid moved. The pore characteristics are stable, whether dry or wet, with minimal, preferably less than about 25%, more particularly 20%, and still more particularly 15%, swelling or collapse when wetted with the visco-elastic fluid simulant. All of these properties are critical to the overall performance of distribution materials placed in the target area of personal care products such as feminine hygiene products.
Current fluid transfer delay layers employed in personal care absorbent articles allow transfer of fluid from the fluid intake/distribution layer to the pad layer resulting in fluid saturation levels of essentially 0.86/g/g/in in the intake distribution layer and/or fluid saturation levels of 0.067 g/g/in the pad layer. Personal care articles which demonstrate relatively high levels of saturation in the intake/distribution layer and relatively low levels of saturation in the pad layer as measured using the flat system testing procedure often have relatively high intake times and high rewet values such as those measured with the intake/rewet test. The fluid transfer delay layer employed in the personal care absorbent article of this invention enables fluid transfer from the intake/distribution layer to the pad layer while still allowing fluid distribution by the fluid intake/distribution layer along the machine direction of the article. This results in a fluid saturation level of less than or equal to about 0.86 g/g/in in the fluid intake/distribution material and/or a fluid saturation level essentially equal to or greater than 0.06 g/g/in in the pad layer. Fluid transfer delay is generally accomplished by the fluid transfer delay layer having a lower density than the fluid intake/distribution layer.